Hazard

A hazard is anything that can hinder the gameplay, except for monsters. Hazards can directly damage or kill the player, or make actions such as movement difficult. Hazards present an additional challenge for the player and form what various game manuals refer to as dangerous or damaging enviroment.

Doom games
Doom introduced several hazards:
 * barrels that explode after being shot, dealing damage to everything in the blast radius;
 * crushing ceiling that can damage or kill the player and monsters standing under it;
 * damaging floor that represents the effect of touching dangerous liquids such as lava or nukage.

Doom 64, in addition to the above, also features the following:
 * dart launchers which can be found and activated as traps throughout some of the maps;
 * homing fireballs which are also encountered and activated as traps.

Heretic
Heretic inherited crushing ceilings and damaging floors from Doom, but also introduced several new hazards:
 * carrying sectors in the form of wind or water currents, which can disrupt the player's movement, as well as affect the trail of some projectiles;
 * ice floors on which the player slides;
 * the pod that is similar to the Doom's exploding barrel, but with the addition of a special pod generator thing that can spawn pods;
 * the volcano, a new thing that is usually placed in lava, it launches fireballs into the air that fall down and explode into smaller fireballs. Both can deal damage to the player and monsters.

Hexen
Hexen inherited the hazards from Heretic (with the exception of pods and volcanoes), but also added a few new ones:
 * falling from a great height can now injure or even kill the player;
 * the mushroom, another variant of the exploding barrel, but instead of exploding, it spawns a cloud of poisonous gas that can damage both the player and monsters;
 * the spike that can instantly kill a player or monster that steps on it;
 * several variants of deadly traps. A few examples: at the beginning of the Winnowing Hall there are walls that shoot fireballs, in the Castle of Grief there are walls that shoot darts and fireballs, and a floor that shoots volcano fireballs.

Strife
Strife introduced several hazards:
 * its own variant of the exploding barrel;
 * falling from a great height can injure or even kill the player;
 * force field, a special type of obstacle.

Hacx
Hacx introduced several hazards:
 * electron;
 * nitro canister;
 * pulsar.

Doom 3
Doom 3 features the following hazards that are reminiscent of their counterparts in the original games:
 * exploding barrels;
 * falling damage;
 * damaging floors.

There are also some new hazards:
 * bottomless pits that can instantly kill the player;
 * burning gas coming out of broken pipes;
 * the atmosphere of Mars - there are several sections where the player goes outside the base and must monitor the air supply;
 * toxic gases - in one level of Doom 3: Resurrection of Evil the player has to proceed through waste tunnels using the enviro suit. This hazard resembles the previous one. It was removed in Doom 3: BFG Edition.